Dose calibrator linearity test: 99mTc versus 18F radioisotopes

Objective: The present study was aimed at evaluating the viability of replacing 18F with 99mTc in dose calibrator linearity testing. Materials and Methods: The test was performed with sources of 99mTc (62 GBq) and 18F (12 GBq) whose activities were measured up to values lower than 1 MBq. Ratios and deviations between experimental and theoretical 99mTc and 18F sources activities were calculated and subsequently compared. Results: Mean deviations between experimental and theoretical 99mTc and 18F sources activities were 0.56 (± 1.79)% and 0.92 (± 1.19)%, respectively. The mean ratio between activities indicated by the device for the 99mTc source as measured with the equipment pre-calibrated to measure 99mTc and 18F was 3.42 (± 0.06), and for the 18F source this ratio was 3.39 (± 0.05), values considered constant over the measurement time. Conclusion: The results of the linearity test using 99mTc were compatible with those obtained with the 18F source, indicating the viability of utilizing both radioisotopes in dose calibrator linearity testing. Such information in association with the high potential of radiation exposure and costs involved in 18F acquisition suggest 99mTc as the element of choice to perform dose calibrator linearity tests in centers that use 18F, without any detriment to the procedure as well as to the quality of the nuclear medicine service.

Constitutive laws for strong geometric non-linearity

This paper is divided into two different parts. The first one provides a brief introduction to the fractal geometry with some simple illustrations in fluid mechanics. We thought it would be helpful to introduce the reader into this relatively new approach to mechanics that has not been sufficiently explored by engineers yet. Although in fluid mechanics, mainly in problems of percolation and binary flows, the use of fractals has gained some attention, the same is not true for solid mechanics, from the best of our knowledge. The second part deals with the mechanical behavior of thin wires subjected to very large deformations. It is shown that starting to a plausible conjecture it is possible to find global constitutive equations correlating geometrical end energy variables with the fractal dimension of the solid subjected to large deformations. It is pointed out the need to complement the present proposal with experimental work.

Close relationship between diameters at 30cm height and at breast height (DBH)

This paper proposes the establishment of a second diameter measuring standard at 30cm shoot extension ('diam30') as input variable for allometric biomass estimation of small and mid-sized plant shoots. This diameter standard is better suited than the diameter at breast height (DBH, i.e. diameter at 1.30m shoot extension) for adequate characterization of plant dimensions in low bushy vegetation or in primary forest undergrowth. The relationships between both diameter standards are established based on a dataset of 8645 tree, liana and palm shoots in secondary and primary forests of central Amazonia (ranging from 1-150mm dbh). Dbh can be predicted from the diam(30) with high precision, the error introduced by diameter transformation is only 2-3% for trees and palms, and 5% for lianas. This is well acceptable for most field study purposes. Relationships deviate slightly from linearity and differ between growth forms. Relationships were markedly similar for different vegetation types (low secondary regrowth vs. primary forests), soils, and selected genera or species. This points to a general validity and applicability of diameter transformations for other field studies. This study provides researchers with a tool for the allometric estimation of biomass in low or structurally heterogeneous vegetation. Rather than applying a uniform diameter standard, the measuring position which best represents the respective plant can be decided on shoot-by-shoot. Plant diameters measured at 30cm height can be transformed to dbh for subsequent allometric biomass estimation. We recommend the use of these diameter transformations only for plants extending well beyond the theoretical minimum shoot length (i.e., >2m height). This study also prepares the ground for the comparability and compatability of future allometric equations specifically developed for small- to mid-sized vegetation components (i.e., bushes, undergrowth) which are based on the diam(30) measuring standard.

Optimisation of a quantitative polymerase chain reaction-based strategy for the detection and quantification of human herpesvirus 6 DNA in patients undergoing allogeneic haematopoietic stem cell transplantation

Human herpesvirus 6 (HHV-6) may cause severe complications after haematopoietic stem cell transplantation (HSCT). Monitoring this virus and providing precise, rapid and early diagnosis of related clinical diseases, constitute essential measures to improve outcomes. A prospective survey on the incidence and clinical features of HHV-6 infections after HSCT has not yet been conducted in Brazilian patients and the impact of this infection on HSCT outcome remains unclear. A rapid test based on real-time quantitative polymerase chain reaction (qPCR) has been optimised to screen and quantify clinical samples for HHV-6. The detection step was based on reaction with TaqMan® hydrolysis probes. A set of previously described primers and probes have been tested to evaluate efficiency, sensitivity and reproducibility. The target efficiency range was 91.4% with linearity ranging from 10-106 copies/reaction and a limit of detection of five copies/reaction or 250 copies/mL of plasma. The qPCR assay developed in the present study was simple, rapid and sensitive, allowing the detection of a wide range of HHV-6 loads. In conclusion, this test may be useful as a practical tool to help elucidate the clinical relevance of HHV-6 infection and reactivation in different scenarios and to determine the need for surveillance.

Determinação de pesticidas organofosforados em água usando microextração em fase sólida e CGAR-EM

Solid-phase microextraction (SPME) has been applied to direct extraction of 11 organophosphorus pesticides in water using a 100 mm fiber polydimethylsiloxane. The method was evaluated with respect time of exposure, detection limits (LODs), linearity and precision. The detection limits (S/N = 3) depend of each pesticide and varie about ng/L levels. The linearity was satisfactory with coefficients of correlation usually greater than 0.993. The precision of the method was determined by extraction from 4.0 mg/L aqueous standard with coefficients of variation between 5.7 to 17.2%.

Determinação enzimática de dopamina em formulações farmacêuticas utilizando sistema de análise por injeção em fluxo com extrato bruto de abacate (Persea americana)

In this work, a spectrophotometric flow injection analysis system using a crude extract of avocado (Persea americana) as a source of polyphenol oxidase to dopamine determination was developed. The substrates and enzyme concentrations from 2.4x10-7 to 5.3x10-4 mol L-1 and 28 to 332 units mL-1 were evaluated, respectively. In addition, the FIA parameters such as sample loop (50 to 500 µL), flow rate (1.4 to 4.3 mL min-1) and reactor length (100 to 500 cm) were also evaluated in a 0.1 mol L-1 phosphate buffer solution (pH 7.0). Dopamine solution concentrations were determined using 277 units mL-1 enzyme solution, 400 mL enzyme loop, 375 µL sample loop, 2.2 mL min-1 flow rate and a reactor of 350 cm. The analytical curve showed a linearity from 5.3x10-5 to 5.3x10-4 mol L-1 dopamine with a detection limit of 1.3x10-5 mol L-1. The analytical frequency was 46 h-1 and the RSD lower than 0.5% for 5.3x10-4 mol L-1 dopamine solution (n=10). A paired t-test showed that all results obtained for dopamine in commercial formulations using the proposed flow injection procedure and a spectrophotometric procedure agree at the 95% confidence level.

Análise química quantitativa para a padronização do óleo de copaíba por cromatografia em fase gasosa de alta resolução

Quantitative GC-FID was evaluated for analysis of methylated copaiba oils, using trans-(-)-caryophyllene or methyl copalate as external standards. Analytical curves showed good linearity and reproducibility in terms of correlation coefficients (0.9992 and 0.996, respectively) and relative standard deviation (< 3%). Quantification of sesquiterpenes and diterpenic acids were performed with each standard, separately. When compared with the integrator response normalization, the standardization was statistically similar for the case of methyl copalate, but the response of trans-(-)-caryophyllene was statistically (P < 0.05) different. This method showed to be suitable for classification and quality control of commercial samples of the oils.

Validation and statistical analysis of two high performance liquid chromatography methods for the determination of indinavir sulfate raw material and capsules

Two high performance liquid chromatography (HPLC) methods for the quantitative determination of indinavir sulfate were tested, validated and statistically compared. Assays were carried out using as mobile phases mixtures of dibutylammonium phosphate buffer pH 6.5 and acetonitrile (55:45) at 1 mL/min or citrate buffer pH 5 and acetonitrile (60:40) at 1 mL/min, an octylsilane column (RP-8) and a UV spectrophotometric detector at 260 nm. Both methods showed good sensitivity, linearity, precision and accuracy. The statistical analysis using the t-student test for the determination of indinavir sulfate raw material and capsules indicated no statistically significant difference between the two methods.

Development and validation of an alternative titration method for the determination of sulfate ion in indinavir sulfate

A simple and rapid precipitation titration method was developed and validated to determine sulfate ion content in indinavir sulfate raw material. 0.1 mol L-1 lead nitrate volumetric solution was used as titrant employing potentiometric endpoint determination using a lead-specific electrode. The United States Pharmacopoeia Forum indicates a potentiometric method for sulfate ion quantitation using 0.1 mol L-1 lead perchlorate as titrant. Both methods were validated concerning linearity, precision and accuracy, yielding good results. The sulfate ion content found by the two validated methods was compared by the statistical t-student test, indicating that there was no statistically significant difference between the methods.

Sorção e persistência da sorgoleona em um Latossolo Vermelho-Amarelo

The root exudates produced by sorghum contain a biologically active constituent known as sorgoleone. The behavior of sorgoleone in a Red-Yellow Latosol was studied. The sorption model of sorgoleone in soil was better adjusted to the Freundlich equation, through the coefficients Kf (capacity of sorption) and 1/n (linearity of the isotherm). The persistence of sorgoleone in soil and its possible degradation were also evaluated by monitoring their residues in the soil along the time. Recovery rate of sorgoleone from the soil reached 93% after 24h. It was verified that sorgoleone is strongly sorbed in the soil and its half-life is 10 days, under the experimental conditions. The presence of sorgoleone or its metabolites was not detected in the soil after 60 days.

Análise de praguicidas organofosforados em água por extração em fase sólida (SPE) utilizando discos C18 e cromatografia em fase gasosa: avaliação da contaminação do reservatório de Furnas (MG-Brasil)

Solid phase extraction (SPE) in C18 disks has been optimized and validated for extraction of 5 organophosphorus (OP) pesticides in water. Extraction has been followed by separation and detection by gas chromatography/flame photometry. Excellent linearity was obtained for all compounds (r greater than 0.99), with CVs between 1.0-6.9%, recoveries between 73-95% and quantification limits between 2.5-5.0 µg L-1. Samples from Furnas dam were analyzed monthly during one year and 10% showed OP pesticide residues.

Determinação indireta de N-acetil-L-cisteína por injeção em fluxo empregando Ce(IV) e ferroína

An indirect flow injection spectrophotometric procedure is proposed for the determination of N-acetyl-L-cysteine in pharmaceutical formulations. In this system, ferroin ([Fe(II)-(fen)2]2+) in excess, with a strong absorption at 500 nm, is oxidized by cerium(IV) yielding cerium(III) and [Fe(III)-(fen)2]3+ (colorless), thus producing a baseline. When N-acetyl-L-cysteine solution is introduced into the flow injection system, it reacts with cerium(IV) increasing the analytical signal in proportion to the drug concentration. Under optimal experimental conditions, the linearity of the analytical curve for N-acetyl-L-cysteine ranged from 6.5x10-6 to 1.3x10-4 mol L-1. The detection limit was 5.0x10-6 mol L-1and recoveries between 98.0 and 106% were obtained. The sampling frequency was 60 determinations per hour and the RSD was smaller than 1.4% for 2.2x10-5 mol L-1 N-acetyl-L-cysteine.

Metodologia para análise simultânea de ácido nicotínico, trigonelina, ácido clorogênico e cafeína em café torrado por cromatografia líquida de alta eficiência

A reverse phase liquid chromatography method was developed for simultaneous determination of trigonelline, caffeine, nicotinic and chlorogenic (5-CQA) acids in roasted coffee. A gradient of acetic acid/acetonitrile was used as mobile phase and detection was carried out in the UV. The samples were extracted with acetonitrile/water (5:95 v/v) at 80 ºC/10 min. Good recovery (89 to 104%), repeatability and linearity were obtained. Detection limits of 0.01, 0.15, 0.04 and 0.04 mg mL-1 were observed for nicotinic acid, trigonelline, 5-CQA and caffeine. The method, applied to arabica and robusta coffees with different degrees of roasting, was efficient and fast (~35 min) and also allowed identification of cinnamic acids.

Determinação de zinco em solo utilizando colorimetria

In terms of soil fertility, zinc is a micronutrient that is very important in the culture of soy, maize, rice and coffee, because it is a structural and functional component of a great number of enzymes. Therefore, diverse methods have been used to determine zinc in soil. In this work we use colorimetry as a methods of zinc determination in soil using two methodologies of sample digesting, H2SO4/H2O2 and HNO3/H2O2. In order to compare the results, atomic absorption spectrometry (AAS) was used. Results show that colorimetric methods can be used due to good sensitivity and reproducibility, since the zinc calibration curve showed good linearity. Comparing colorimetric methods with AAS we observed that the results were equivalent, as proven by the statistical values of the F and t of Student tests. Furthermore, both methods of soil digesting can be used, leading to a flexible methodology of low-cost for routine zinc analyses in soil.

Um estudo teórico relativo à não-linearidade da ligação de hidrogênio em sistemas heterocíclicos C2H4O-C2H2 e C2H4S-C2H2

B3LYP/6-31G(d,p) calculations were used to determine the optimized geometries of the C2H4O-C2H2 and C2H4S-C2H2 heterocyclic hydrogen-bonded complexes. Results of structural, rotational, electronic and vibrational parameters indicate that the hydrogen bonding is non-linear due to the pi bond of the acetylene interacting with the hydrogen atoms of the methyl groups of the three-membered rings. Moreover, the theoretical investigation showed that the non-linearity is much more intriguing, since there is a structural disjunction on the acetylene within the heterocyclic system.